Re: 2.0.11 on OS X 10.9 / Xcode 5.1

[Taylan Ulrich Bayirli/Kammer]

Taylan Ulrich Bayirli/Kammer <address@hidden> writes:

> The next roadblock I hit is that when I run gdb on the guile
> executable, it doesn't seem to realize that the libguile dylib is
> loaded, so still lacks the debug symbols from it.  (When I enter "info
> sharedlibrary" it says "No shared libraries loaded at this time"
> although the Guile REPL and all runs, so libguile is obviously
> loaded.)  I'll continue tomorrow if I have time again at work.

Update:

I gave up on gdb on OS X and tried the native lldb, which essentially
worked but failed to print relevant stack variables (maybe because of
-O2).  I resorted to printf debugging, but at least had immediate
success!

I can reproduce the problem with the following minimal program, compiled
with -O1 (not necessarily -O2):

/* BEGIN */
#include <stdio.h>
#include <math.h>

int main (int argc)
{
  double ang = 0, s, c;

  /* Prevent constant-propagation. */
  /* (Program must be called with no arguments.) */
  if (argc == 1)
    ang = -0.0;

  s = sin (ang);
  c = cos (ang); /* This line is needed to reproduce. */

  printf("%f\n", s); /* Prints "0.000000". */

  return c /* Prevent c from being optimized out. */;
}
/* END */

I don't know why `c' and/or the `cos (ang)' call are needed, but I fail
to reproduce the bug after only slight, seemingly irrelevant changes.

With the native clang on the system, the bug can't be reproduced.

Channel #gcc on Freenode suggested trying out -m32 vs. -m64, and
-mfpmath=387 vs. -mfpmath=sse, but the bug persists with all
combinations.

I also tried out other GCC packages of MacPorts: GCC 4.3 through 4.9 all
have the bug.  The plain GCC 4.2 package is not supported on recent OS X
versions.  Apple-patched GCC 4.2 does *not* have the bug.  (There are no
more recent Apple-patched GCC versions.)

I suppose I should move this to the GCC mailing list?

Taylan